Magnetic head assembly



Feb. l, 1966 w. D. Mol-:HRING MAGNETIC HEAD ASSEMBLY Filed Nov. 4, 1960 United States Patent Ofi ice 3,23346 Patented Feb. l, 1966 3,233,046 MAGNETEC HEAD ASSEMBLY William l). Moelxrng, 211 Pleasant St., Charlotte, Mich. Filed Nov. 4, 1966, Ser. No. 67,221 S Claims. (Cl. 179-100.@

This invention relates to improvements in magnetic head assembly. The principal objects of the invention are:

First, to provide a magnetic erase head which can be easily manufactured to close dimensional tolerances to provide uniformity in a Series of mass produced heads.

Second, to provide a magnetic erase head in which the gap between the poles of the magnetic circuit is formed by cutting or grinding away parts of the magnetic circuit which are initially in contact to locate the parts during assembly.

Third, to provide a novel method of manufacturing a magnetic erase head in which the magnetic parts are assembled in predetermined positions established by stamping operations which can be accurately controlled, after which the parts are permanently secured together by a solidifying insulating resin and the pole gaps of the magnetic circuit are formed by cutting away the contacting portions of the magnetic elements to expose gap forming portions of the insulating material.

Fourth, to provide a magnetic erase head in which a magnetic core and coacting magnetic housing are automatically retained in accurately controlled preselected positions my inherent spring pressure in the housing during the assembly of the head.

Other objects and advantages of the invention will be apparent from a consideration of the following description and claims.

The drawings, of which there is one sheet, illustrate a highly practical form of the erase head and the several steps of the process of manufacturing the same.

FlG. l is a front elevational view of the assembly and finished head.

FIG. 2 is a cross sectional view through one of the cores of the head taken along the plane of the line 2 2 in FIG. 1.

FIG. 3 is an enlarged fragmentary cross sectional View of the gap area of the core and housing shown in FIG. 2.

FIG. 4 is a plan view of a blank used for forming the housing in FIGS. 2 and 3.

FIG. 5 is a plan view of the housing in partially assembled position with the core and coil parts of the head and the housing illustrated in dotted lines in assembled position.

FIG. 6 is a fragmentary enlarged cross sectional view of the core and adjacent housing parts in assembled position prior to formation of the magnetic gap around the core.

FIG. 7 is an enlarged fragmentary cross sectional View through the core-receiving opening taken along the plane of the line 7-7 in FIG. 4.

The magnetic erase head and its method of assembly disclosed herein constitute improvements over the similar structure disclosed in U.S. Patent No. 2,950,355 issued August 23, 1960. The present erase head is illustrated as having two cores 1 and 2, arranged in adjacent positions for acting upon two lparts or tracks of a single magnetic tape. The head consists of an inner boxshaped housing 3 which may be further enclosed in a surrounding mass of solidified epoxy resin 4 in a mounting ca-se 5. Each core 1 and 2 is surrounded by an electrical coil 6 and the forward ends of the cores are projected to a curved face 7 ground on the exposed open face of the resin at one side of the case 5. Terminal connections from the coils 6 may be extended to the exterior of the case in any suitable fashion and are not illustrated. If desired, the outer case 5 and enclosed insulating resin 4 may be omitted with the housing 3 then forming the exterior of the head.

The invention lies in the structure and method of assembly of the housing 3 and the parts therein.

As appears most clearly in FIG. 4, the housing 3 is formed from an elongated strip 8 of magnetic conductive material such as soft iron. The strip is sized to provide a central forward face or Wall 9, side walls 1@ and 11 and back walls 12 and 13. The strip is folded along fold lines 14 into the wall sections mentioned. Prior to folding and conveniently as part of the forming operation of the strip 8, upper slots 1S and 4lower slots 16 are formed in the end walls 12 and 13 and two flanged holes 17 and 18 are extruded or folded from the front wall 9. The holes 17 and 18 can be formed in Various manners and to illustrate two examples of satisfactory structures, the hole 17 is illustrated with a complete annular forwardly extruded flange 19 therearound such as may be formed by pressing a properly sized and shaped die into the rear face of the wall 9. The hole 18 differs slightly in that it is formed by blanking out a central opening with diagonally extending slits 2t) at its edges and then folding the intervening flanges forwardly as at 21. Either the annular flange 19 or the flanges 21 are shaped in outwardly converging relation as along the radius line 22 and by proper selection of the forming die, the space between these flanges and the shape of the converging portions Z2 are easily and accurately controlled to tit and locate the forward ends of the cores 1 and 2 at the narrowest part of the opening as shown in FEG. 6.

After the anged holes 17 and 18 are formed, the strip 8 is folded into box shape as shown in FIG. 5 with the forward Wall 9 desirably slightly convex. The core bars 1 and 2 with the coils 6 therearound are inserted into the openings 17 and 18 and the rear walls 12 and 13 are drawn into overlapping relation until the slots 15 and 16 are in registry. The rear ends of the cores 1 and 2 are inserted in the slots 1S and 16 so that the cores keep the strip from unfolding and the resiliency in the strip assures firm magnetic contact between the rear walls of the strip and the cores. After the cores, coils and strip are assembled, the interior of the box-shaped housing 3 is filled with a thermo setting insulating plastic material such as an epoxy resin as at 23 with care being taken to extend the the insulating plastic into the converging area between the radius lines 22 and the sides of the core bars. After the plastic insulating material has solidified, the extruded projecting anges 19 and 21 can be cut or ground away along with the forward ends of the core bars 1 and 2 to the planes of the lines a-rz or b-b in FIG, 6. It will be evident that this grinding away will remove the area of contact between the forward ends of the core bars and the surrounding anges 19 or 21 to expose an annular gap surface 24 of insulating material completely around the core bars. The width of this gap surface will be determined and can be accurately controlled by the depth to which the flanges 19 are cut away; for example cutting to the line a-a will provide a larger or wider gap than ilzyvoubld be formed if the cutting away stopped at line As was previously mentioned, the folded housing 3 with the core bars, coils and retaining insulation 23 therein may be used as a finished head assembly or the entire housing may be further enclosed in the casing 5 and surrounding plastic 4. Since the accuracy of the location of the several parts of the head is determined by the relative size and positions of the core bars, core bar openings 17 and f8 and the slots 15 and 16 and since all of these positions and sizes can be accurately controlled by using a single set of dies, it is evident that a series of hear structures manufactured fr-om the same `set of dies will have substantially uniform magnetic properties and that the assembly of successive head structures can be easily accomplished with the parts automatically assuming the proper positions in the head assembly.

I have illustrated and described my invention in a highly practical embodiment thereof. I have not attempted to illustrate or describe other adaptations or embodiments which I contemplate, as I believe this disclosure will enable those skilled in the art to embody 0r adapt my invention as may be desired.

What is claimed as new is:

l. A magnetic erase head assembly comprising a housing formed of a continuous strip of magnetically conductive material folded in box shape with a convex front wall and overlapped ends forming the rear Wall, a pair of holes spaced from top to bottom in said front wall and completely within the outline of the wall, registering slots formed in the upper and lower edges of the overlapping ends in said rear wall and located oppoiste said holes, a pair of magnetic core bars having their forward ends received =in said holes and having their rear ends received in said registering slots, electrical coils positioned around said cores within asid housing and a mass of solidified insulating Vepoxy resin material lling said housing around said cores and coils, the inner surface of said front wall being angled arcuately outwardly around siad cores with a narrow band o-f said insulating material separating said cores from said Wall.

2. A magnetic erase head assembly comprising a` housing formed of a continuous strip of magnetically conductive material folded in box shape with a front wall and overlapped ends forming the rear wall, a pair of holes spaced from the top to bottom in said front wall and completely within the outline of the wall, registering slots formed in the upper and lower edges of the overlapping ends in said rear wall and located opposite said holes, a pair of magnetic core bars having their forward ends received in said holes and having their rear ends received in said registering slots, electrical coils positioned around said cores within said housing and a mass of solidified insulatng material filling siad housing around said cores and coils, the inner surface of said front wall being angled outwardly around said cores with a narrow band of said insulating material separating said cores from said Wall.

3. A magnetic erase head assembly comprising a housing formed of a continuous strip of magnetically -conductive material folded in box shape with a front wall and overlapped ends forming the rear wall, a hole in said front wall and completely within the outline of the wall, registering slots formed in the edges of the overlapping ends in said rear wall and located opposite said hole, a magnetically conductive core bar having its forward end received' in said hole and having its rear end received in contacting engagement with the edges of said registeringv slots, an electrical coil positioned around said core Within said housing and a mass of solidified insulating material filling said housing around'said core and coil,

Cil

the inner surface of said front wall being angled outwardly around said core with a narrow band of said insulating material separating said core from said wall.

4. A magnetic erase head assembly comprising'a housing formed `of a continuous strip of magnetically conductive material folded in box shape with a front wall and overlapped ends forming the roar wall, a hole in said front wall and completely within the outline of the wall, registering openings formed in the overlapping ends in said rear wall and located opposite said hole, a magnetically conductive core bar having its forward end received in said hole and having its rear end received in contacting engagement with the edges of said registering openings, an electrical coil positioned around said core within said housing and a mass Iof solidified insulating materal filling said housing around said core and coil, the inner surface of said front wall being angled outwardly on opposite sides of said core with a narrow band `of said insulating material separating said core from said wall.

5. In a magnetic head, a strip of magnetically conductive metal forming the front wall of a magnetically conductive housing and defining an yopening completely within the outline of said front wall, a core bar of magnetically conductive metal having its forward end projecting through said opening and having its rear end engaged in contacting relation to the rear of said housing, the inner surface of said strip around said opening being converged outwardly of said opening and spaced from said core bar, a coil positioned around said core bar in magnetizing relation to the magnetic circuit formed by said bar and said housing, and a mass of solid insulating material solidied in situ in said housing extending into the converging space between said core and said strip with a band of the insulating material exposed around and finished flush with the outer end of said core.

6. In a magnetic head, a strip of magnetically conductive metal forming the front wall of a magnetically conductive housing and dening an opening, a core bar of magnetically conductive metal having its forward end projecting through said opening and having its rear end engaged in contacting relation to the rear of said housing, the inner surface of said strip on opposite sides of said opening being converged outwardly of said opening and spaced from said core bar, .a coil positioned in magnetizing relation to the magnetic circuit formed by said bar and said housing, and a mass of solid insulating material in said housing extending into the converging space between said core and said strip with a band of the insulating material exposed around and finished ush with the outer end of said core.

7. In a magnetic head, a housing having integral magnetically conductive front, side and rear walls, said front Wall defining .an opening with opposed outwardly converging interior surfaces on all sides of said opening, a core bar of magnetically conductive material having its front end in said opening and having it-s rear end in magnetically conducting relation to said rear wall to complete a magnetic circuit through said bar and said walls, a coil arranged around said bar in magnetically inductive relation to said circuit, and a mass of magnetically non-conductive material solidified around said bar and coil within said housing and extending into the space defined by the sides of said bar and said interior converging surfaces around said opening, the outer side of said front wall and the front end of said core bar being finished along a common surface intersecting said mass of magnetically non-conductive material around said bar to provide a gap in said magnetic circuit.

8. linY a magnetic head, a housing `having Vintegral magnetically conductive front, side and rear walls, said front wall defining an opening with opposed Voutwardly converging interior surfaces, a core bar of magnetically conductive material having its front end in said opening and having its rear end in magnetically conducting rela- 'c1011. Q Said rear Wall t-o complete a magnetic circuit through said bar and said Walls, a coil arranged in magnetically inductive relation to said circuit, and a mass of magneticaily non-conductive material solidified around said bar and coil within said housing and extending into the space dened by the sides of said bar and ysaid interior 5 References Cited by the Examiner UNITED STATES PATENTS 2,674,031 4/ 1954 Buhrendorf 29-155.57

Buhrendorf 179-1002 Buhrendorf 29-155.58

Buhrendorf 179-1002 Moehring 179-1002 Frost 179-1002 X FOREIGN PATENTS Germany.

0 IRVING L. SRAGOW, Primary Examiner.

NEWTON N. LOVEWELL, Examiner. 

1. A MAGNETIC ERASE HEAD ASSEMBLY COMPRISING A HOUSING FORMED OF A CONTINUOUS STRIP OF MAGNETICALLY CONDUCTIVE MATERIAL IN BOX SHAPE WITH A CONVEX FRONT WALL AND OVERALAPPED ENDS FORMING THE REAR WALL, A PAIR OF HOLES SPACED FROM TOP TO BOTTOM IN SAID FRONT WALL AND COMPLETELY WITHIN THE OUTLINE OF THE WALL, REGISTERING SLOTS FORMED IN THE UPPER AND LOWER EDGES OF THE OVERLAPPING ENDS IN SAID REAR WALL AND LOCATED OPPOSITE SAID HOLES, A PAIR OF MAGNETIC CORE BARS HAVING THEIR FORWARD ENDS RECEIVED IN SAID HOLES AND HAVING THEIR REAR ENDS 